The Asteroid that is Spinning Itself to Oblivion

The Hubble Space Telescope has spotted an asteroid spinning so quickly that it is throwing material off its surface, dooming the body to destruction. A pair of comet-like tails emanating from this active asteroid, named Gault, reveal two instances when the asteroid has lost a significant amount of material to space.

Asteroid (6478) Gault was discovered in 1988, but new observations from Hubble and other observatories show the asteroid is falling apart due to uneven heating from the Sun. This breakup of material allows researchers an opportunity to study the composition of the asteroid, without a need to send a spacecraft to the body.

“We didn’t have to go to Gault. We just had to look at the image of the streamers, and we can see all of the dust grains well-sorted by size. All the large grains (about the size of sand particles) are close to the object and the smallest grains (about the size of flour grains) are the farthest away because they are being pushed fastest by pressure from sunlight,” said Olivier Hainaut of the European Southern Observatory, a member of the Gault observation team.

The Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect takes place when sunlight heats small bodies in space, resulting in the release of heat — and momentum — from the object. This creates a small amount of torque, which can result in an increased rate of spin for the body. This, in turn, adds to the centrifugal force experienced by materials on the surface, resulting in the release of rubble and dust into space. If the object starts to spin more than once every two hours, centrifugal force will overcome gravity, and the affected body can fall apart. Gault is believed to be spinning right at this critical two-hour rate.

Within the asteroid belt between Mars and Jupiter, containing 800,000 bodies, astronomers estimate that an average of one active asteroid like Gault are destroyed each year through the YORP effect.

The asteroid belt between Mars and Jupiter contains roughly 800,000 objects, ranging in size from dust particles to the dwarf planet Ceres, large enough to hold on to a thin atmosphere. Image credit: ESA/ATG medialab

“This self-destruction event is rare. Active and unstable asteroids such as Gault are only now being detected by means of new survey telescopes that scan the entire sky, which means asteroids such as Gault that are misbehaving cannot escape detection any more,” Olivier Hainaut of the European Southern Observatory explains.

Exploring Gault’s Gulch

Gault stretches roughly four kilometers (2.5 miles) from side to side, and revolves around the Sun at a distance of roughly 344 million kilometers (214 million miles) from our parent star. Researchers believe the asteroid has been spinning due to the YORP effect for roughly 100 million years.

The longer tail reaches more than 800,000 kilometers (500,000 miles) in length, and is around 4,800 kilometers (3,000 miles) wide. The smaller of the two tails is approximately one quarter of that size. Each of the features will last just a few months, before the material disperses to surrounding space.

Observations by Hubble of the region around Gault do not reveal any widespread debris, eliminating the possibility that the tails are the result of a collision between Gault and another body.

Observations of the features suggest the tails formed from material released from the asteroid around October 28 and December 30, 2018. Each event lasted between a few hours and a few days, together releasing enough material to form a ball 150 meters (500 feet) in diameter.

In addition to the Hubble Space Telescope, a wide range of observatories contributed to the discovery of the odd behavior of Gault, including the ATLAS and Pan-STARRS telescopes in Hawaii, as well as the Issac Newton Telescope in Spain.